In modern communication systems, there is an ever-increasing demand for smaller and more versatile portable terminals, e.g., hand-portable telephones. It is well known that the size of an antenna is a critical factor for its performance. Further, the interaction between antenna, telephone body and proximate environment, e.g., the user, will become more important than ever. Recently, there is also normally a requirement that two or more frequency bands be supported. It is thus a formidable task to manufacture such compact and versatile terminals, which exhibit good antenna performance under a variety of conditions.
Current manufacturing of a hand-portable telephone commonly adapts the antenna to the characteristics of this specific telephone and to be suited for a default use in a default environment. This means that the antenna cannot later on be adapted to any specific condition under which a certain telephone is to be used or to suit a different hand-portable telephone. Thus, each model of a hand-portable telephone must be provided with a specifically designed antenna, which normally cannot be optimally used in any other telephone model.
The radiating properties of an antenna device for a hand-held wireless communication device depends heavily on the shape and size of the support structure such as a printed circuit board (PCB) of the device and of the telephone casing. All radiation properties, such as resonance frequency, input impedance, bandwidth, radiation pattern, gain, polarization, and near-field pattern are a product of the antenna device itself and its interaction with the PCB and the telephone casing. Thus, all references to radiation properties made below are intended to be for the whole device in which the antenna is incorporated.
What has been stated above is true also with respect to other radio communication devices, such as cordless telephones, telemetry systems, wireless data terminals, etc. Thus, the antenna device of the invention is applicable on a broad scale in various communication devices.
Receiving antennas, with diversity functionality, which can adapt to various radio wave environments, are known. Such diversity functionality systems may be used to suppress noise, and/or undesired signals such as delayed signals, which may cause inter-symbol interference, and co-channel interfering signals, and thus improve the signal quality. However, these diversity functioning antennas require complex receiver circuitry structure, including multiple receiver chains, and a plurality of antenna input ports.
Switchable antennas are known in the literature for achieving diversity. In such switchable antennas, certain characteristics of the antenna system can be varied by connecting/disconnecting segments of the dipole arms to make them longer or shorter, for instance.
However, none of the above arrangements provide any switchable antenna elements that are connected or disconnected on some intelligent basis, e.g. when needed due to signal conditions.